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Beam-hardening artifacts resulting from heavily calcified plaques in patients with a high coronary calcium score (CCS) may reduce coronary computed tomography angiography (CTA) diagnostic accuracy of the increased false-positive rate (1). A recently introduced computed tomography (CT) technology combines dual-energy computed tomography (DECT) with the latest gemstone detectors, made by a complex rare earth–based oxide that has a chemically replicated garnet crystal structure for gemstone spectral imaging (GSI) integrated into a 64-slice scanner (1). The scanner is equipped with an x-ray source that can switch energy rapidly. The datasets obtained from 2 different energies allow the reconstruction of material decomposed images (MDIs). Two studies demonstrated that coronary CTA using the new DECT offers improvement in terms of image quality compared with standard single-energy CT (1,2). The aim of the present study was to evaluate in patients with a high CCS (>400) the diagnostic accuracy of coronary CTA using DECT with monochromatic images and calcium removal by MDI compared with simulated conventional polychromatic image evaluation as a simulated standard of reference (sSTD) and compare the results with invasive coronary angiography (ICA). We enrolled 75 patients with indication for nonemergent ICA for suspected coronary artery disease (CAD), a CCS higher than 400, and a heart rate of ≤65 beats/min. Coronary CTA was performed with GSI-capable CT (Discovery HDCT 750, GE Healthcare, Milwaukee, Wisconsin) and the followings parameters: 64 × 0.625 mm and gantry rotation time of 0.35 s. Cardiac GSI can simultaneously acquire data by rapidly switching between 80 kVp and 140 kVp energies in <0.252 ms, which produces data that contain minimal misregistration artifacts. The beam was kept at 140 kVp for only a fraction (about one-third) of the radiation time to keep the radiation dose low, whereas during two-thirds of the scan time, the beam was switched to a lower tube current peak (80 kVp). A tube current of ≅600 mA was used. All scans were performed with prospectively electrocardiography-triggered acquisition. First, from the acquired DECT data, conventional polychromatic images that corresponded to a peak tube voltage ranging between standard values of 100 kV and 120 kV were simulated using a 77-keV monochromatic image and used as an sSTD. Second, MDI (iodine minus calcium) derived from the GSI data were used to represent the GSI. The Adaptive Statistical Iterative Reconstruction (ASIR) post-processing algorithm (set at 40%) was used for both types of image reconstruction (sSTD and GSI). The pre-test probability of CAD was intermediate to high (62%). Accordingly, the prevalence of obstructive CAD was 68% (51 of 75 patients). Of patients with ≥50% stenosis, 31 (61%) had multivessel CAD. The mean CCS was 606 ± 253. Eighty percent of patients were pre-treated with intravenous metoprolol before scanning, achieving a mean heart rate of 59 ± 5 beats/min. The mean effective dose was 0.87 mSv for CCS and 3.92 mSv for coronary CTA. The number of coronary segments with excellent image quality was significantly higher with GSI (57%) than with sSTD reconstruction (48%). The overall coronary evaluability was significantly higher after calcium removal compared with sSTD evaluation (98.2% vs. 94.9%) due to a lower number of severe artifacts (n = 21 vs. n = 61, respectively). In a subanalysis of artifacts, we found a significantly lower number of beam-hardening artifacts with MDI (n = 6) compared with sSTD (n = 46). In a segment-based analysis, coronary CTA sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy for more than 50% coronary stenosis identification were 100%, 99.3%, 93.8%, 100%, and 99.4%, respectively, with GSI and 100%, 95.9%, 66.4%, 100%, and 96.1%, respectively, with sSTD. Specificity, PPV, and accuracy were significantly higher with GSI compared with sSTD. In a patient-based analysis, coronary CTA sensitivity, specificity, PPV, NPV, and accuracy were 100%, 88.8%, 94.1%, 100%, and 96.2%, respectively, with GSI and 93.7%, 11.1%, 65.2%, 50% and 64.4%, respectively, with sSTD. Specificity, PPV, NPV, and accuracy were significantly higher with GSI compared with sSTD. Our study is the first to evaluate the diagnostic performance of coronary CTA performed with rapid kilovolt peak–switching DECT and MDI evaluation in patients referred for ICA. The main finding is that GSI technology allows a significant improvement of coronary CTA image quality, evaluability, and diagnostic accuracy versus simulated conventional polychromatic images reconstructed in the same patients (Figure 1). This remarkable improvement was the result of the combined use of monochromatic images at different energies, which per se determine beam-hardening reduction, as previously demonstrated, and calcium removal by MDI. Last, the radiation exposure of the new approach is substantially lower (mean effective dose <4 mSv).

Footnotes

Please note: Dr. Pontone is on the Speakers Bureau of GE Healthcare, Bayer, HeartFlow, and Medtronic; and is a consultant for Heartflow. Dr. Andreini is on the Speakers Bureau of GE Healthcare. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.